There is an increasing demand for alkylate fuel blending feedstock. As a fuel-blending component alkylate combines a low vapour pressure, no sulfur, olefins or aromatics with high octane properties. The most desirable components in the alkylate are trimethylpentanes (TMPs), which have research octane numbers (RONs) of greater than 100. Such an alkylate component may be produced by reacting isobutane with a butene in the presence of a suitable acidic catalyst, e.g. HF or sulfuric acid, although other catalysts such a solid acid catalyst have been reported. Recently, the alkylation of isoparaffins with olefins using an acidic ionic liquid catalyst has been proposed as an alternative to HF and sulfuric acid catalysed alkylation processes.
For instance, U.S. Pat. No. 7,285,698 discloses a process for manufacturing an alkylate oil, which uses a composite ionic liquid catalyst to react isobutane with a butene. In the process of U.S. Pat. No. 7,285,698, isobutane and a butene are supplied to a reactor and the alkylate is formed by contacting the reactants with a composite ionic liquid under alkylation conditions. The reactor effluent is separated and the ionic liquid phase is recycled to the reactor while the hydrocarbon phase is treated to retrieve the alkylate. It has however been found that during operation of an ionic liquid alkylation process, solids are formed. As the reaction progresses, these solids accumulate in the reaction zone and may lead to blockage of pathways and/or valves. In WO2011/015639 a process is described for removal of the solids formed during the ionic liquid alkylation process. According to that process, the solids are completely removed and disposed of. This is economically unfavourable and very undesirable from an environmental point of view. Therefore, there is a need for (at least partial) regeneration of the solids formed in the ionic liquid alkylation process.